Recently, with the increasing development of information industries, portable information devices such as notebook computers, mobile phones or personal digital assistants are widely used in many instances. In case that a portable information device is used in a dim environment, the numbers and the characters marked on the keys of the keyboard of the portable information device are not clearly visible. In other words, the dim environment becomes hindrance from operating the keyboard. In addition, if the numbers and the characters marked on the keys of the keyboard are reluctantly viewed in the dim environment, the user is readily suffered from vision impairment. For solving these drawbacks, a luminous keyboard has been introduced into the market. The luminous keyboard can be used in the dim environment in order to enhance the applications thereof. Moreover, by changing the luminous layout of the luminous keyboard, the information device having the luminous keyboard is more aesthetically-pleasing and thus the competitiveness thereof is enhanced.
FIG. 1 is a schematic cross-sectional view illustrating a conventional luminous keyboard. FIG. 2 is a schematic perspective view illustrating a membrane wiring board and a keyboard circuit board of the conventional luminous keyboard of FIG. 1. FIG. 3 schematically illustrates optical paths within a light guide plate of the membrane wiring board of the conventional luminous keyboard of FIG. 1. As shown in FIGS. 1, 2 and 3, the conventional luminous keyboard 1 comprises a reflective plate 11, a light guide plate 12, a metallic supporting plate 13, a membrane wiring board 14, plural keys 15, and at least one light-emitting element 16. The membrane wiring board 14 comprises a lower wiring plate 141, an upper wiring plate 142, and an intermediate plate 143. The intermediate plate 143 is arranged between the lower wiring plate 141 and the upper wiring plate 142. The lower wiring plate 141, the intermediate plate 143 and the upper wiring plate 142 are all made of a transparent material.
The lower wiring plate 141 comprises a first circuit pattern 1411. The first circuit pattern 1411 comprises plural silver paste conductor lines 14111 and plural lower contacts 14112. The upper wiring plate 142 comprises a second circuit pattern 1421. The second circuit pattern 1421 comprises plural silver paste conductor lines 14211 and plural upper contacts 14212. The intermediate plate 143 comprises plural perforations 1431 corresponding to the plural lower contacts 14112 and the plural upper contacts 14212, respectively. Each of the upper contacts 14212 and the corresponding lower contact 14112 are collectively defined as a membrane switch 144.
The metallic supporting plate 13 is disposed under the membrane wiring board 14 for connecting the plural keys 15. In addition, the metallic supporting plate 13 comprises plural supporting plate openings 131 corresponding to the plural keys 15. Each of the keys 15 is disposed over a corresponding membrane switch 144. As any key 15 is depressed and moved downwardly, the corresponding membrane switch 144 is pushed by the key 15, and thus the corresponding membrane switch 144 is electrically conducted. Under this circumstance, the luminous keyboard 1 generates a corresponding key signal.
Moreover, the light-emitting element 16 is located at a lateral side of the light guide plate 12 for emitting a light beam into the light guide plate 12. The light guide plate 12 is disposed on the reflective plate 11. Moreover, plural light-guiding dots 121 are formed on a bottom surface of the light guide plate 12 for collecting and scattering the light beams. The light-guiding dots 121 are aligned with corresponding keys 15. After the light beam is introduced into the light guide plate 12, the light beam is diffused within the whole light guide plate 12. A portion L11 of the light beam is projected onto the light-guiding dots 121. Due to the ink properties of the light-guiding dots 121, the portion L11 of the light beam will be scattered upwardly and downwardly. The portion of the light beam that is scattered upwardly (L111) will be sequentially transmitted through the plural supporting plate openings 131 of the metallic supporting plate 13 and the membrane wiring board 14 and then projected to the plural keys 15. The portion of the light beam that is scattered downwardly (L112) will be reflected by the reflective plate 11, and the reflected light beam L112 is directed upwardly. Consequently, the light beam provided by the light-emitting element 16 can be well utilized. Under this circumstance, the purpose of illuminating the plural keys 15 is achieved.
However, the conventional luminous keyboard 1 still has some drawbacks. For example, after the light beam is introduced into the light guide plate 12, since the incidence angle of a portion L12 of the light beam is very small, the advancing direction of the portion L12 of the light beam is substantially in parallel with an optical axis of the light-emitting element 16. In other words, the portion L12 of the light beam fails to be projected onto the light-guiding dots 121. Under this circumstance, the portion L12 of the light beam fails to be guided from the light guide plate 12 to the plural keys 15, and thus the light utilization efficiency of the conventional luminous keyboard 1 is usually unsatisfied.
Therefore, there is a need of providing an improved luminous keyboard in order to eliminate the above drawbacks.